The present invention relates to a valve arrangement for obtaining an unloading liquid flow for cooling a centrifugal pump or the like even when working against a closed supply pipe. The arrangement includes a valve housing containing a non-return valve, the respective closing and opening movement of the non-return valve causing a respective opening and closing of an unloading orifice in the valve housing, such that an unloading liquid flow will be obtained even when the non-return valve is in a closed position within the valve housing.